Seatbelts, such as those used in the automotive industry, are commonly provided with a spring biased retractor spool. Such a retractor automatically retracts the seatbelt webbing onto the spool to the extent that the spring bias force is not overcome by an extension force applied to the webbing. Therefore, the webbing will be automatically retracted onto the spool if the seatbelt is removed by the passenger. Additionally, if the passenger is wearing the seatbelt, the spring biased retractor will automatically size the seat belt to the passenger by removing any slack from the seatbelt. Except during the situations described hereinbelow, the webbing may be extended from the retractor whenever enough force is applied to the webbing to overcome the spring bias force of the retractor.
In order for the seatbelt to retain the passenger in the seat during an emergency situation, however, it is necessary for the retractor to lock and thereby prevent any further extension of the webbing from the retractor. This type of device is known as an emergency locking retractor. The emergency locking feature is generally activated in two different ways. First, the retractor is fitted with a webbing sensor which senses rapid extension of the webbing from the retractor and locks the retractor in response thereto. The webbing sensor is generally a flyweight which moves m response to rapid rotation of the retractor, causing an adjacent pawl to engage a toothed surface of the retractor, thereby preventing further extension of the webbing from the retractor.
A second type of emergency locking feature is provided by fitting the retractor with a vehicle sensor, which senses rapid acceleration or deceleration of the vehicle. The vehicle sensor is generally a metal ball which is confined within an enclosed space. Any rapid acceleration or deceleration of the vehicle will cause the metal ball to be displaced from its normal resting position, thereby activating a retractor locking mechanism.
Such prior art emergency locking retractors provide important safety benefits, however they do exhibit some undesirable characteristics. For example, if the vehicle is parked on a slant from the horizontal, then it is possible for the metal ball of the vehicle sensor to be displaced from its normal resting position, thereby triggering the emergency locking feature of the retractor. Any attempt to withdraw the webbing from the retractor will be unsuccessful, preventing the seatbelt from being worn until the vehicle is moved to a suitably less inclined attitude.
Another problem results when the emergency locking retractor is not locked by the vehicle sensor and the webbing is rapidly withdrawn with such force as to trigger the webbing sensor. Further withdrawal will be prevented, causing frustration to the heavy handed user and discouraging the use of the seatbelt.
A further problem can result if the webbing is allowed to retract rapidly into an emergency locking retractor, coming to a stop at the fully retracted position. In this situation, the webbing sensor may be forced into the locking mode, thereby preventing all subsequent withdrawal of the webbing and rendering the seatbelt inoperative.
A further problem with the prior art emergency locking retractors results from the prior art design of the vehicle sensor. A typical prior art emergency locking retractor is illustrated in U.S. Pat. No. 4,522,350 to Ernst, which is illustrated in FIG. 1 and indicated generally at 1. The prior art retractor 1 includes a vehicle sensor which uses a ball actuator 2, wherein a metal ball 3 is mounted in a saucer like receptacle 4 having sloping sides. When acceleration or deceleration of the vehicle is applied to the vehicle sensor 2, the ball 3 is caused to roll up the side walls of the saucer 4 at a predetermined acceleration level which is dependent upon the angle of the side walls of the saucer 4. Riding over the top of the ball is a saucer shaped cap 5 which is mounted on one side by a jointed pair of pivot bearings 6. The upper portion of the cap 5 includes a reaching ball tip 7 which engages the locking mechanisms of the retractor 1. Upon displacement of the ball 3 from its resting position, the ball 3 will ride up the side walls of the saucer 4, displacing the cap 5 and forcing the pawl 8 to be displaced upwards, thus engaging the pawl 8 into the ratchet teeth 9 of the locking mechanism. The retractor 1 is shown in its locked position in FIG. 2. The conical shape of the cap 5 which engages the top of the ball 3 also aids in this upward movement.
Experience has shown that this prior art device has an inherent problem, particularly on vehicles where the vehicle sensor 2 is mounted in a position distant to the center of gravity of the vehicle. In this location, it is possible for the vehicle sensor 2 to be excited in a vertical direction by accelerations exceeding 1 g. For instance, if the vehicle sensor 2 is accelerated downwards, the ball 13 is left behind and suspended in space, thus driving the pawl 8 upwards into engagement with the locking mechanism 9. This result is undesirable in that it causes the retractor 1 to lock when the vehicle is traveling at a constant horizontal velocity, and under these conditions, locking is not desirable.
Finally, withdrawal forces applied to the webbing of a locked prior art retractor in an emergency situation are transmitted to the components of the sensor in the locking initiation mechanism. A retractor design which isolates the sensor and locking initiation mechanism from webbing withdrawal forces would be a substantial improvement over the prior art designs.
There is therefore a need in the prior art for an emergency locking seatbelt retractor which allows the seatbelt to be applied by the passenger when the vehicle is parked and inclined from the horizontal, which allows the webbing to be withdrawn by the user at a very rapid pace without locking the retractor prior to application of the seatbelt to the passenger, which will not lock-up when the webbing is allowed to retract rapidly into the retractor, which will not lock when the vehicle accelerates in a downward direction, and which isolates the sensor and locking initiation mechanism from webbing withdrawal forces. The present invention is directed toward meeting these needs.